Ion implantation is a technique for introducing property-altering impurities into substrates. During a typical ion implantation process, a desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of a substrate. The energetic ions in the ion beam penetrate into the sub-surface of the substrate material and are embedded into the crystalline lattice of the substrate material to form a region of desired conductivity or material property. The process of embedding or implanting ions into the crystalline lattice of the substrate material is also known as “doping” the substrate.
An ion implanter may generate an ion beam having a roughly circular or elliptical cross sectional shape that is smaller than the surface of a substrate to be treated. A substrate, which may be a semiconductor, for example, may have a round, disk shape. A substrate scanning device or substrate scanning device may dope a substrate, such as a substrate, by exposing it to the ion beam generated by the ion implanter.
In order to implant ions into the entire surface of a substrate, the substrate may be mechanically driven or “scanned” in a direction along a scan axis that is orthogonal to the direction of an ion beam projected thereon. For example, if an ion beam is projected along a horizontal plane toward a vertically-oriented substrate, the substrate may be scanned in a vertical direction and/or in a lateral direction that is perpendicular to the projected ion beam.
The entire surface of the substrate may be exposed to the relatively smaller ion beam during an implantation process. The substrate scanning device serially exposes portions of the substrate surface to the ion beam. The implantation process is completed when the substrate has been doped with a predetermined “dose” of ions. Proper dosing is a delicate and precise process. Dose non-uniformities occur when portions of a substrate surface are exposed to the ion beam for varying amounts of time. Dose non-uniformities can result in a substrate with undesirable characteristics and poor performance.
Substrate scanning devices require excellent velocity performance to uniformly expose portions of a substrate, such as the surface of a substrate, to an ion beam and minimize dose non-uniformities. Inconsistent velocity performance can cause portions of a substrate surface to be exposed to the ion beam for varying amounts of time and result in dose non-uniformities in substrates. As manufacturing standards steadily increase, substrate scanning devices with improved velocity control, accuracy, and dexterity are needed to uniformly dope substrates in a quick and efficient manner. Thus, it would be advantageous to provide a solution for doping substrates in a uniform manner. An additional advantage would be to provide a solution for scanning a substrate at a constant velocity. It would be advantageous to provide a solution to exposing portions of a substrate to an ion beam predetermined amount of time. It would also be advantageous to provide a solution for quickly and efficiently doping substrates.